"I couldn't believe when I opened it, just all those little heads right there," Dr. Frank Mills said. "They were on top of each other."

It's the third time in a little more than three months that a box like this was dropped at the animal hospital. Mills thinks the cats in the most recent box came from two litters.

The kittens' hair was matted with feces and their eyes were filled with pus. Mills brought them inside and set out to bring them back to health, as he had with the last seven cats abandoned in two groups in his parking lot beginning in August.

He said he hopes media attention will keep whoever is leaving the cats from doing so again.

Mills said the timing of the three dropoffs seems to line up with the length of a cat's pregnancy, so he thinks it's possible the kittens could come from one or two animals with the same owner. He doesn't know who left the boxes.

All of the kittens were about 6 weeks old, roughly the age at which a mother cat stops nursing. The first two groups of kittens were so sickly when they arrived that Mills feared they would be euthanized if he took them to a shelter. Instead, he paid for their care out of pocket. They were spayed or neutered, vaccinated and treated for fleas and worms.

"I have several hundred dollars, it seems like, invested in every cat," Mills said.

He plans to treat this new group of kittens in the same way.

Of seven cats he had tended to before Tuesday, one died and two were adopted. Four more remain available for adoption at Pasadena Veterinary Hospital, at 7000 Central Ave. in St. Petersburg, for a $75 fee.

Claire Wiseman can be reached at cwiseman@tampabay.com or (727)-893-8804. Follow @clairelwiseman on Twitter.

CHERIE DIEZ | Times

Dr. Frank Mills of Pasadena Veterinary Hospital holds four of the 9 kittens he found in a box in the parking lot of the hospital Wednesday morning.